Abstract: Pterocarpus marsupium Roxb. is a medicinally important tree of the family Fabaceae with a long history of traditional use and a diverse phytochemical profile. The present investigation was undertaken to evaluate and compare the antimicrobial potential of different in vivo plant tissues and in vitro-derived tissues of P. marsupium against selected bacterial pathogens. The study formed the fourth objective of a broader research programme involving mass multiplication, phytochemical profiling, pharmacological evaluation and molecular characterization of the species. Leaf, stem, bark, fresh callus, old callus and whole-plant/in vitro-derived material were evaluated against seven bacterial microorganisms, namely Bacillus subtilis, Escherichia coli, Enterobacter aerogenes, Proteus vulgaris, Pseudomonas aeruginosa, Shigella boydii and Salmonella paratyphi. Antimicrobial activity was assessed from zones of inhibition using the agar well/cup diffusion approach described in the thesis. Marked variation was observed among plant tissues, extract treatments and microorganisms. Bark and callus tissues generally demonstrated stronger activity than roots and several other tissues. Particularly high inhibition zones included 36.0 ± 0.27 mm against E. coli, 35.0 ± 0.21 mm against S. boydii and 27.0 ± 0.25 mm against B. subtilis in selected preparations. S. boydii was the most susceptible organism overall, whereas P. aeruginosa was comparatively resistant. Fresh and old callus demonstrated substantial activity, indicating that in vitro culture can retain or enhance the production of antimicrobial metabolites. Statistical analysis reported in the thesis showed significant treatment differences for several extract-organism combinations, with p-values as low as 0.0001. The antimicrobial responses are discussed in relation to the distribution of phenolics, flavonoids, tannins, saponins, quinones and other secondary metabolites documented elsewhere in the thesis. The findings support the pharmacological potential of P. marsupium and highlight in vitro tissues as promising material for further investigation of plant-derived antimicrobial compounds.

Keywords: Pterocarpus marsupium; antimicrobial activity; antibacterial activity; bark; callus; phytochemicals; agar well diffusion; medicinal plant; in vitro culture.